Type of facial expressions used exclusively when facing another individual, those used exclusively when not facing another individual, and those that occurred in both facing and non-facing situations.

For more details on the morphology regarding previous descriptions of these facial expressions, see S2 Table. All facial expressions including AU10, AU16, AU25, AU26, AU27 are forms of ‘open-mouth’ displays [23]. Frequencies and other details are reported in S2 and S3 Tables.